Some prior art semiconductor devices employ an electrode structure, such as shown in FIGS. 1 and 2. The semiconductor device shown in FIGS. 1 and 2 includes a semiconductor layer 11 of a III-V compound semiconductor, such as GaAs and InP. A semiconductor layer 12 is disposed on a major surface of the semiconductor layer 11. The plane orientation of the major surface is (100). The semiconductor layer 12 is also a III-V compound semiconductor, such as GaAs and InP and has an edge extending along the [010] direction, as shown in FIG. 2. The orientation of the plane of the side surface 14 of the edge is (001) which is orthogonal to the major surface of the semiconductor layer 11. The semiconductor layer 12 is formed by epitaxially growing a semiconductor layer over the entire major surface of the semiconductor layer 11 and, using a mask, etching away undesired portions of the epitaxially grown semiconductor layer until the portions of the major surface of the layer 11 beneath them are revealed. An electrode 13 is disposed on both of the major surfaces of the semiconductor layers 12 and 11. The electrode 13 is formed by vacuum vapor depositing a metal onto the major surfaces of the semiconductors layers 11 and 12 from the direction perpendicular thereto, so that the electrode 13 has a step presenting a side surface 16 near the side surface 14 of the semiconductor layer 12, as shown in FIG. 2.
Because the electrode 13 is formed by vacuum vapor deposition in the direction perpendicular to the major surfaces of the semiconductor layers 11 and 12, the distance t.sub.s of the side surface 16 of the conductor electrode 13 from the extension of the side surface 14 of the semiconductor layer 12 is substantially smaller than the thickness t.sub.o of that portion of the conductor electrode 13 which lies on the major surface of the semiconductor layer 12. In an extreme situation, the distance t.sub.s may be zero and, therefore, the conductor electrode 13 may be discontinuous. One may contemplate use of a sputtering technique, instead of vacuum vapor deposition, trying to form the electrode 13 with a larger t.sub.s, since, in sputtering, the mean free path of film forming particles is small and, accordingly, a relatively large number of the film forming particles tend to turn around corners. However, such film forming particles still impinge perpendicularly to the major surface of the semiconductor layers 11 and 12, and, therefore, the distance t.sub.s is only 10-20% of the thickness t.sub.o. Furthermore, due to some etching conditions, poor adhesion of an etching mask used to mask the semiconductor layer 12, the orientation of the side surface 14 may sometimes be displaced from its desired (001) orientation so that the ratio t.sub.s /t.sub.o may vary considerably depending on etching conditions. If the distance t.sub.s small, when a current I is applied to the electrode 3, since the resistance of the electrode 13 at the portion with the thickness t.sub.s is large, the Joule heat Q generated at that portion, which is expressed as Q=I.sup.2 R, becomes large. Ultimately, the temperature at the portion may reach the melting point of the material of the conductor electrode 13, so that part of the electrode 13 melts and becomes discontinuous.
An object of the present invention is to provide a semiconductor device with a large distance t.sub.s to avoid disconnection of parts of the electrode 13, and also a method of making such a semiconductor device.
In order to achieve the above-identified object, the semiconductor device according to the present invention comprises a layer of a III-V compound semiconductor material having a major surface in the (100) orientation, which has a side surface formed by etching the major surface. The semiconductor device also includes an electrode disposed on said semiconductor layer passing over said side surface. The side surface of the semiconductor layer beneath the electrode includes at least one region with an [011] orientation and a surface with a (111) orientation.
A method of making a semiconductor device of the above-described type includes etching a III-V compound semiconductor layer from its (100) oriented major surface with a mask including at least one region with an [011] orientation to form a step in the semiconductor layer, and depositing an electrode material on the semiconductor layer from a direction perpendicular to the major surface to form an electrode crossing the step in the semiconductor layer.